1. Field of the Invention
This invention relates to an optical system for a color television camera, and more particularly to an optical system for a color television camera provided with an interchangeable taking lens.
2. Description of the Prior Art
In a color television camera, a color separating prism block is located behind a taking lens system and three image pick-up tubes are located behind the color separating prism block for three colors, i.e. red, green and blue. The axial position of the three image pick-up tubes is controlled to always obtain sharp images on their image receiving face. In order to finely control the axial position of the image pick-up tubes, there have been employed tracking means in each tube in the conventional color television cameras.
The positions of the focal planes of the three different color images are different from each other due to the chromatic aberration. In other words, the focal planes of the three different color images are not optically conjugate with each other because of the difference in refractive indices for different wavelengths. Further, the difference in position of the focal planes is proportional to the focal length of the taking lens system. Therefore, even if the positions of the three image pick-up tubes are once axially determined to obtain sharp images on all the tubes for one taking lens of a focal length, the position must be readjusted when the taking lens is changed to one of a different focal length.
Therefore, in case of a television camera in which the taking lens is interchangeable, the axial position of the image pick-up tubes must be readjusted every time the taking lens is changed. However, it is very difficult and requires a complicated costly means to smoothly and accurately adjust the axial position of the image pick-up tubes.